Copper-Mediated Remote C-H Bond Chalcogenation of Quinolines on the C5 Position

Article abstract of DOI:10.1021/acs.orglett.5b02511

An efficient and convenient method is developed for the remote C-H bond chalcogenation of 8-aminoquinoline scaffolds on the C5 position that is geometrically inaccessible. The protocol makes use of inexpensive CuBr₂ as mediator and shows good t

Full text of DOI:10.1021/acs.orglett.5b02511

Letter
pubs.acs.org/OrgLett
Copper-Mediated Remote C−H Bond Chalcogenation of Quinolines
on the C5 Position
Longzhi Zhu,† Renhua Qiu,*,† Xin Cao,† Song Xiao,† Xinhua Xu,† Chak-Tong Au,†,‡
and Shuang-Feng Yin*,†
†State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University,
Changsha 410082, P. R. China
‡Department of Chemistry, Hong Kong Baptist University, Hong Kong, P.R. China
S
* Supporting Information
ABSTRACT: An efficient and convenient method is developed for
the remote C−H bond chalcogenation of 8-aminoquinoline scaffolds
on the C5 position that is geometrically inaccessible. The protocol
makes use of inexpensive CuBr2 as mediator and shows good tolerance
toward numerous disulfides/diselenides and aliphatic amides, giving
the corresponding products in good to excellent yield.
uinolines are skeletons common in natural products and
Scheme 1. Direct Modification of Geometrically Inaccessible
C5 Position of Quinolines
1
Q bioactive molecules (Figure 1). They can be used as
Figure 1. Representative biologically active compounds.
bidentate directing groups or as ligands participating in various
kinds of organic reactions.2 It should be noted that quinolines
are also used as fluorescent probes to detect Zn2+ and Fe3+3 and
are even utilized for fluorescence imaging in living cells.4
Although highly efficient traditional classic methods,5 such as
metal-catalyzed coupling cyclization and acid-catalyzed cyclo-
addition of appropriate anilines as precursors with carbonyl
compounds or alkynes, have been reported,6 the modification
of quinolines, especially those with readily accessible quinoline
frameworks, on the C5 position has rarely been reported.7
Because of the electron effect of quinolines, it is difficult to
control the regioselectivity. Examples of the modification of
quinoline scaffolds are mainly on the C2,8 C3,9 C4,10 and C811
positions that are easily accessible. As for the C5 position that is
geometrically inaccessible, it was not until very recently that its
chlorination was first reported by Stahl et al.,7a followed by Xie
and Zhang et al.7b (Scheme 1a). Furthermore, Zeng and co-
workers7c described the regiodivergent C−H allylation of
quinolines on the C5 position that was enabled by 8-amino and
catalyzed by iron via remote C−H activation (Scheme 1b).12
However, as for the remote C−H chalcogenation of quinolines
on C5 position, there was no disclosed example.7e,f
it is desirable and challenging to develop methods that are
efficient for the synthesis of quinolines aryl chalcogenoethers
on the C5 position from readily available and simple substrates,
preferably using transition metals as catalysts. Generally, the
coupling of RZH (Z = S or Se, hereinafter) or RZZR with
halides catalyzed by a transition metal enables C−Z bond
formation.14 The addition reaction of Z−Z or Z−H bonds with
alkynes or alkenes is another method.15 The method of C−H
bond chalcogenation employing a C−H bond as a trans-
formable functional group allows the shortening of reaction
pathways, thus leading to efficient production of the desired
substances.16 Another important feature of C−H bond
chalcogenation is the ability to achieve unique regioselectivity
that is often unattainable by employing classical methods such
as Friedel−Crafts chemistry.17 As part of our continuing efforts
on the search for C−Z coupling,7f,18 we studied the thiolation
of inactive methyl C(sp3)−H bonds of aliphatic amides with
disulfide over transition-metal catalysts.18b During the inves-
tigation, we observed copper(II)-mediated remote C−H bond
chalcogenation that selectively builds up the 5-arylthio/alkythio
to form quinolines thioethers/selenoethers (Scheme 1c). To
Aryl chalcogenide skeletons are also ubiquitous in bio-
logically active natural products, and they are common in areas
of pharmaceuticals and material science.13 Given the
importance of quinolines and chalcogenides, it is of great
interest to combine the two into a single entity. In this context,
Received: September 1, 2015
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.5b02511
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Letter
a
the best of our knowledge, such a result has never been
reported before.
Scheme 3. Investigation of Disulfide Scope
Initially, N-(quinolin-8-yl)pivalamide (1a) and diphenyl
disulfide (2a) were selected as substrates for the optimization
of reaction conditions (Scheme 2). When the reaction was
a
Scheme 2. Optimization of Reaction Conditions
a
Reaction conditions: 1a (0.3 mmol), 2 (0.36 mmol), CuBr2 (0.45
mmol), DMF (1 mL), isolated yield.
electron-withdrawing group at the p-position of the phenyl ring
performed as well in good to excellent yields under the
optimized (standard) conditions (3a−i). The reaction showed
good tolerance toward a wide range of functional groups such
as methyl, methoxy, halogen, and nitro groups attached to
diaryl disulfides. Notably, the diphenyl disulfides with nitro at
the o-, m-, or p-position gave the corresponding products in
similar yield, which is different from the thiolation of
quinones21 and carbazoles.18a Similar to substituted diaryl
disulfides, dialkyl disulfides such as dicyclohexyl disulfide and
dipropyl disulfide proceeded smoothly to yield the desired
products in moderate yields (3j and 3k).
a
Reaction conditions: 1 (0.3 mmol), 2a (0.36 mmol), copper salt,
b
As depicted in Scheme 4, we explored the reactions of
disulfides with several kinds of 8-aminoquinoline derivatives.
solvent (1.0 mL), O2 atmosphere; GC yield, using n-tridecane as
internal standard; the number in parentheses is isolated yield. 2 equiv
of AgNO3 was added. 2 equiv of K2S2O8 was added. 2 equiv of
PhI(OAc)2 was added. Under N2.
c
d
e
f
a
Scheme 4. Investigation of Aliphatic Amide Scope
carried out at 160 °C for 24 h in the presence of a catalytic
amount of CuBr2 (0.1 equiv) under O2 atmosphere using DMF
as solvent, N-(5-(phenylthio)quinolin-8-yl)pivalamide 3a,
which was a result of quinoline thiolation at the C5 position,
was generated in 10% yield as the only product (entry 1). The
use of CuCl2 and CuI showed similar reactivity, while CuO,
Cu(OTf)2, and copper powder were found to be less effective
(entries 2−6). When the amount of CuBr2 was 2 equiv, there
was 8% yield of the byproduct N-(5-bromoquinolin-8-yl)-
pivalamide 3a′ (entry 7). The structure of thiolated product N-
(5-(phenylthio)quinolin-8-yl)pivalamide 3a was confirmed by
single-crystal X-ray analysis (see the structure in Scheme 2).19
It was found that 1.5 equiv of CuBr2 is the best choice for
avoiding the byproduct (entries 7−11 and Table S1,
Supporting Information). When the reaction was conducted
with basic and acid additives (see Tables S2 and S3, SI), there
was a decline of reactivity. The results are different from that
reported on acid-promoted thiolation reactions catalyzed by
nickel catalysts.20 Further screening showed that DMF is the
most suitable solvent for the reaction (entries 12−15). It was
observed that the lowering of reaction temperature from 160 to
120 °C results in an increase of byproduct N-(5-bromoquino-
lin-8-yl)pivalamide 3a′ (entries 16 and 17, up to 40%). The
presence of N2 enabled a somewhat lower yield relative to
aerobic reaction conditions (entry 18) implies the oxygen may
be benefit for the reaction.7a
a
Reaction conditions: 1 (0.3 mmol), 2 (0.36 mmol), CuBr2 (0.45
b
mmol), DMF (1 mL), isolated yield. 2.5 equiv of PhSSPh was used.
Replacement of tert-butyl with other alkyl groups results in the
desired products in good to excellent yield (4a−p). It is noted
that cycloalkanes such as those with a cyclopentyl or cyclohexyl
group proceeded well (4j−m,n). For those with long-chain
alkyl groups, the thiolation reaction goes smoothly as well (4o
and 4p). Interestingly, when there is a bromide attached to the
alkyl chain, there is one-pot generation of double-thiolation
product (4p). In other words, the strategy offers a way to
achieve double thiolation of quinoline derivatives by remote
C−H thiolation and simple cross-coupling reaction.
Encouraged by the viability of the protocol for direct C−S
bond formation on quinolines, we applied the system to diaryl
diselenides with an aliphatic amide, and the desired C−Se
cross-coupling compounds 5a−g were obtained in good yields
With the optimized reaction conditions in hand, we
investigated the substrate scope with respect to disulfides
(Scheme 3). Diaryl disulfides with an electron-donating or
B
DOI: 10.1021/acs.orglett.5b02511
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(Scheme 5). However, when ditellurides were used under the
standard conditions, the desired products could only be
obtained in very low efficiency.
a cascade reaction after brominated but rather one that is direct
C−H remote thiolation in nature. Furthermore, an intermo-
lecular competition experiment between 2c and 2d was
conducted (Scheme 7c), and it was observed that the
electron-rich disulfide shows a higher reaction rate (3c, 38%;
3d, 8%). We found that the thiolation does not go with 1aa to
yield 9 at all and goes rather ineffectively to 1ab and 1ac,
obtaining 10 and 11 with low yield and regioselectivity,
respectively (Scheme 7d), implying that there is the generation
of an essential copper-center intermediate in the reaction and
the nitrogen atom in the quinoline motif is essential for
improving the regioselectivity.
a
Scheme 5. Investigation of Diselenide Scope
Based on the above results and those reported in the
literature,7,16m we propose a possible pathway for thiolation
that takes place on the C5 position of quinolines (Scheme 8).
a
Reaction conditions: 1 (0.3 mmol), diaryl diselenides (0.36 mmol),
CuBr2 (0.45 mmol), DMF (1 mL), isolated yield.
Scheme 8. Possible Pathway
To demonstrate the synthetic utility of the new method, the
reaction was carried out on a 5 mmol gram scale, and the
desired product was obtained in 65% yield (Scheme 6). The
Scheme 6. Gram Scale and Synthesis Applications
Coordination of the amide 1a to the Cu center forms an
anionic complex A.7a,b Subsequently, the intermolecular SET
between the electron-rich imidoquinoline moieties and the
highly oxidative Cu(II) center occurs, giving the radical
amide bond can be easily broken in 85% yield without
damaging the thioether 3a to obtain 6.18b The thioether 3a can
be oxidized to afford sulfone 7 in 82% yield or further
converted to disulfide 8 in moderate yield according to the
report of Zhang et al.22 and that of ours,18b respectively.
To shed light on the possible pathway of this thiolation
reaction, we performed a number of preliminary experiments as
depicted in Scheme 7. It was found that the addition of
−
complexes B with CuBr2 being reduced to CuBr2 . Then, the
transfer of the PhS group to B occurs, producing the imino−
Cu(II) complex C. Next, the deprotonation of C provides the
thiolated imidate−Cu(II) complex D. The ligand exchange of
D with the starting material 1a affords the C5-thiolated product
3a and regenerates the amidate−Cu(II) anionic complex A for
the next catalytic cycle. Further investigation is being conducted
to provide evidence for the proposed mechanism.
Scheme 7. Control Experiments
In summary, we developed an efficient and convenient
method for C5-chalcogenation of 8-aminoquinoline scaffolds
making use of inexpensive CuBr2. It is possible that the
chalcogention reaction involves a step of remote C−H
activation. The reaction system shows tolerance toward
numerous diaryl/dialkyl disulfides and aliphatic amides, giving
the corresponding products in good to excellent yield. This
protocol can be easily extended to diaryl diselenides in good
yield.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.5b02511.
TEMPO ((2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl) or BHT
(2,6-di-tert-butyl-4-methylphenol) inhibits the reaction, and the
yield is sharply decreased to 42% or trace (Scheme 7a),
suggesting the involvement of a single electron transfer (SET)
pathway in this reaction. Moreover, adduct 12 of the quinoline
radical with BHT was detected by GC−MS.23 An experiment
using the byproduct N-(5-bromoquinolin-8-yl)pivalamide 3a′
to react with PhSSPh resulted in 3a in 15% yield (Scheme 7b),
which excluded the possibility that the brominated product was
a possible intermediate.7 This indicates that the thiolation is not
Detailed experimental procedures, characterization data,
1
spectra copies of the H, 13C NMR (PDF)
X-ray data of 3a (CIF)
AUTHOR INFORMATION
Corresponding Authors
■
*E-mail: renhuaqiu@hnu.edu.cn.
C
DOI: 10.1021/acs.orglett.5b02511
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Letter
(11) (a) Kwak, J.; Kim, M.; Chang, S. J. Am. Chem. Soc. 2011, 133,
3780. (b) Boudet, N.; Lachs, J. R.; Knochel, P. Org. Lett. 2007, 9, 5525.
(12) Selected examples on remote C−H activation: (a) Leow, D.; Li,
G.; Mei, T. S.; Yu, J. Q. Nature 2012, 486, 518. (b) Paterson, A.; St
John-Campbell, S.; Mahon, M. F.; Press, N. J.; Frost, C. G. Chem.
Commun. 2015, 51, 12807. (c) Wan, L.; Dastbaravardeh, N.; Li, G.;
Yu, J. Q. J. Am. Chem. Soc. 2013, 135, 18056. (d) Tang, R. Y.; Li, G.;
Yu, J. Q. Nature 2014, 507, 215. (e) Yu, J.-Q.; Shi, Z. C−H Activation;
Springer: Berlin, 2010.
(13) (a) Lee, M. H.; Yang, Z.; Lim, C. W.; Lee, Y. H.; Dongbang, S.;
Kang, C.; Kim, J. S. Chem. Rev. 2013, 113, 5071. (b) Magano, J.;
Dunetz, J. R. Chem. Rev. 2011, 111, 2177. (c) Mellah, M.; Voituriez,
A.; Schulz, E. Chem. Rev. 2007, 107, 5133.
*E-mail: sf_yin@hnu.edu.cn.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the Natural Science Foundation of China (Nos.
21373003 and 21273068) and the Fundamental Research
Funds for the Central Universities for financial support. R.Q.
thanks Prof. Nobuaki Kambe (Osaka University), Prof. Akihiro
Orita (Okayama University of Science), and Prof. Li-Biao Han
(AIST, Tsukuba) for helpful discussions. C.-T.A. thanks Hunan
University for an adjunct professorship.
(14) (a) Hartwig, J. F. Acc. Chem. Res. 1998, 31, 852. (b) Kondo, T.;
Mitsudo, T-a. Chem. Rev. 2000, 100, 3205. (c) Hartwig, J. F. Acc.
Chem. Res. 2008, 41, 1534. (d) Beletskaya, I. P.; Ananikov, V. P. Chem.
Rev. 2011, 111, 1596.
REFERENCES
■
(1) (a) Michael, J. P. Nat. Prod. Rep. 2008, 25, 166. (b) Kaur, K.; Jain,
M.; Reddy, R. P.; Jain, R. Eur. J. Med. Chem. 2010, 45, 3245.
(c) Colomb, J.; Becker, G.; Fieux, S.; Zimmer, L.; Billard, T. J. Med.
Chem. 2014, 57, 3884. (d) Eicher, T.; Hauptmann, S.; Speicher, A. The
Chemistry of Heterocycles: Structures, Reactions, Synthesis, and
Applications, 3rd ed.; John Wiley & Sons: New York, 2013.
(15) (a) Kuniyasu, H.; Ogawa, A.; Sato, K.; Ryu, I.; Kambe, N.;
Sonoda, N. J. Am. Chem. Soc. 1992, 114, 5902. (b) Iwasaki, M.; Fujii,
T.; Yamamoto, A.; Nakajima, K.; Nishihara, Y. Chem. - Asian J. 2014, 9,
58. (c) Beletskaya, I.; Moberg, C. Chem. Rev. 2006, 106, 2320.
(16) (a) Chen, Z.; Wang, B.; Zhang, J.; Yu, W.; Liu, Z.; Zhang, Y.
Org. Chem. Front. 2015, 2, 1107. (b) Shen, C.; Zhang, P.; Sun, Q.; Bai,
S.; Hor, T. S. A.; Liu, X. Chem. Soc. Rev. 2015, 44, 291. (c) Yan, S.-Y.;
Liu, Y.-J.; Liu, B.; Liu, Y.-H.; Shi, B.-F. Chem. Commun. 2015, 51, 4069.
(d) Yan, X.-B.; Gao, P.; Yang, H.-B.; Li, Y.-X.; Liu, X.-Y.; Liang, Y.-M.
Tetrahedron 2014, 70, 8730. (e) Iwasaki, M.; Kaneshika, W.; Tsuchiya,
Y.; Nakajima, K.; Nishihara, Y. J. Org. Chem. 2014, 79, 11330. (f) Hu,
G.; Xu, J.; Li, P. Org. Lett. 2014, 16, 6036. (g) Du, B.; Jin, B.; Sun, P.
Org. Lett. 2014, 16, 3032. (h) Yang, Y.; Hou, W.; Qin, L.; Du, J.; Feng,
H.; Zhou, B.; Li, Y. Chem. - Eur. J. 2014, 20, 416. (i) Yi, C.-L.; Liu, T.-
J.; Cheng, J.-H.; Lee, C.-F. Eur. J. Org. Chem. 2013, 2013, 3910.
(j) Tran, L. D.; Popov, I.; Daugulis, O. J. Am. Chem. Soc. 2012, 134,
18237. (k) Chu, L.; Yue, X.; Qing, F.-L. Org. Lett. 2010, 12, 1644.
(l) Zhang, S.; Qian, P.; Zhang, M.; Hu, M.; Cheng, J. J. Org. Chem.
2010, 75, 6732. (m) Chen, X.; Hao, X. S.; Goodhue, C. E.; Yu, J. Q. J.
Am. Chem. Soc. 2006, 128, 6790. (n) Iwasaki, M.; Tsuchiya, Y.;
Nakajima, K.; Nishihara, Y. Org. Lett. 2014, 16, 4920.
(2) (a) Zaitsev, V. G.; Shabashov, D.; Daugulis, O. J. Am. Chem. Soc.
2005, 127, 13154. (b) Castro, L. C. M.; Chatani, N. Chem. Lett. 2015,
44, 410. (c) Corbet, M.; De Campo, F. Angew. Chem., Int. Ed. 2013,
52, 9896. (d) Rouquet, G.; Chatani, N. Angew. Chem., Int. Ed. 2013,
52, 11726. (e) Wu, X.; Zhao, Y.; Ge, H. J. Am. Chem. Soc. 2014, 136,
1789. (f) Matsubara, T.; Asako, S.; Ilies, L.; Nakamura, E. J. Am. Chem.
Soc. 2014, 136, 646. (g) Pan, F.; Shen, P. X.; Zhang, L. S.; Wang, X.;
Shi, Z. J. Org. Lett. 2013, 15, 4758. (h) Brunel, J. M.; Del Campo, B.;
Buono, G. Tetrahedron Lett. 1998, 39, 9663. (i) Marcelli, T.; van
Maarseveen, J. H.; Hiemstra, H. Angew. Chem., Int. Ed. 2006, 45, 7496.
(3) (a) Fahrni, C. J.; O’Halloran, T. V. J. Am. Chem. Soc. 1999, 121,
11448. (b) Meng, X. M.; Wang, S. X.; Li, Y. M.; Zhu, M. Z.; Guo, Q.
X. Chem. Commun. 2012, 48, 4196. (c) Huang, J.; Xu, Y.; Qian, X.
Dalton. Trans. 2014, 43, 5983.
(4) (a) McQuade, L. E.; Lippard, S. J. Inorg. Chem. 2010, 49, 7464.
(b) Zhu, S. S.; Lin, W. Y.; Yuan, L. Dyes Pigm. 2013, 99, 465.
(c) Meeusen, J. W.; Tomasiewicz, H.; Nowakowski, A.; Petering, D. H.
Inorg. Chem. 2011, 50, 7563.
(5) (a) Reitsema, R. H. Chem. Rev. 1948, 43, 43. (b) Bergstrom, F.
W. Chem. Rev. 1944, 35, 77. (c) Kouznetsov, V. V.; Men
(17) Friedel, C.; Crafts, J. M. C. R. Hebd. Seances Acad. Sci. 1877, 84,
1450.
(18) (a) Zhu, L.; Cao, X.; Qiu, R.; Iwasaki, T.; Reddy, V. P.; Xu, X.;
Yin, S.-F.; Kambe, N. RSC Adv. 2015, 5, 39358. (b) Wang, X.; Qiu, R.;
Yan, C.; Reddy, V. P.; Zhu, L.; Xu, X.; Yin, S.-F. Org. Lett. 2015, 17,
1970. (c) Qiu, R.; Reddy, V. P.; Iwasaki, T.; Kambe, N. J. Org. Chem.
2015, 80, 367.
(19) Copies of crystallographic data (CCDC 1419167 (3a)) can be
obtained free of charge from the Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
(20) (a) Yang, K.; Wang, Y.; Chen, X.; Kadi, A. A.; Fun, H. K.; Sun,
H.; Zhang, Y.; Lu, H. Chem. Commun. 2015, 51, 3582. (b) Aihara, Y.;
Chatani, N. J. Am. Chem. Soc. 2014, 136, 898.
(21) Zhang, C.; McClure, J.; Chou, C. J. J. Org. Chem. 2015, 80,
4919.
́
dez, L. Y. V.;
Gomez, C. M. M. Curr. Org. Chem. 2005, 9, 141.
́
(6) (a) Kong, L. K.; Zhou, Y. Y.; Huang, H.; Yang, Y.; Liu, Y. Y.; Li,
Y. Z. J. Org. Chem. 2015, 80, 1275. (b) Wang, Y.; Chen, C.; Peng, J.;
Li, M. Angew. Chem., Int. Ed. 2013, 52, 5323. (c) Horn, J.; Marsden, S.
P.; Nelson, A.; House, D.; Weingarten, G. G. Org. Lett. 2008, 10, 4117.
(d) Shaabani, A.; Rahmati, A.; Badri, Z. Catal. Commun. 2008, 9, 13.
(7) Examples on modification of 8-aminoquinoline on the C5
position: (a) Suess, A. M.; Ertem, M. Z.; Cramer, C. J.; Stahl, S. S. J.
Am. Chem. Soc. 2013, 135, 9797. (b) Guo, H.; Chen, M.; Jiang, P.;
Chen, J.; Pan, L.; Wang, M.; Xie, C.; Zhang, Y. Tetrahedron 2015, 71,
70. (c) Cong, X.; Zeng, X. Org. Lett. 2014, 16, 3716. (d) Liang, H.-W.;
Jiang, K.; Ding, W.; Yuan, Y.; Shuai, L.; Chen, Y.-C.; Wei, Y. Chem.
Commun. 2015, DOI: 10.1039/C5CC05527J. Two examples for trace
byproducts: (e) Chen, F.-J.; Zhao, S.; Hu, F.; Chen, K.; Zhang, Q.;
Zhang, S.-Q.; Shi, B.-F. Chem. Sci. 2013, 4, 4187. (f) Reddy, V. P.; Qiu,
R.; Iwasaki, T.; Kambe, N. Org. Biomol. Chem. 2015, 13, 6803.
(8) (a) Berman, A. M.; Lewis, J. C.; Bergman, R. G.; Ellman, J. A. J.
Am. Chem. Soc. 2008, 130, 14926. (b) Tobisu, M.; Hyodo, I.; Chatani,
N. J. Am. Chem. Soc. 2009, 131, 12070. (c) Zhao, D.; Wang, W.; Yang,
F.; Lan, J.; Yang, L.; Gao, G.; You, J. Angew. Chem., Int. Ed. 2009, 48,
3296.
(22) (a) Yu, M.; Xie, Y.; Xie, C.; Zhang, Y. Org. Lett. 2012, 14, 2164.
(b) Yao, J.; Yu, M.; Zhang, Y. Adv. Synth. Catal. 2012, 354, 3205.
(23) (a) Ji, Y.-F.; Zhang, Z.-N.; Huang, J.-G.; Zhai, J.-J.; Guo, Y.
Synlett 2015, 26, 2145. (b) Baik, W.; Lee, H. J.; Jang, J. M.; Koo, S.;
Kim, B. H. J. Org. Chem. 2000, 65, 108.
(9) (a) Wasa, M.; Worrell, B. T.; Yu, J. Q. Angew. Chem., Int. Ed.
2010, 49, 1275. (b) Sun, K.; Lv, Y.; Wang, J.; Sun, J.; Liu, L.; Jia, M.;
Liu, X.; Li, Z.; Wang, X. Org. Lett. 2015, 17, 4408.
(10) (a) Tsai, C.-C.; Shih, W.-C.; Fang, C.-H.; Li, C.-Y.; Ong, T.-G.;
Yap, G. P. J. Am. Chem. Soc. 2010, 132, 11887. (b) Chen, Q.; du
Jourdin, X. M.; Knochel, P. J. Am. Chem. Soc. 2013, 135, 4958.
D
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